Field of the Invention
Embodiments relate to methods of updating a location information, which represents a physical location of a communication device, which is generated by a location source, and which is sent from the location source via a location object generating unit and cache unit to a location consumer. Embodiments further relate to a computer program product for executing such a method and to a communication system for updating the location information.
Background of the Related Art
As part of presence conveyance a location may be associated with a device and/or a user. The physical location of the device may be represented by a location information provided in an element of the device such as a communication device, e. g. a mobile or an IP phone. Presence conveyance may be an important issue in emergency cases: the location information may be used by emergency services such as NG911 (Next Generation 9-1-1) or NG112 (Next Generation 1-1-2) to locate the device that initiated an emergency communication request. Such a location information may be expressed as civic location, e. g. a postal address, and/or as geospatial coordinates, e. g. a map location. The physical location of the device is required in order for a telephony server to locate a suitable emergency services number to be used to place the call (routing). This number is obtained by interrogating a remote Location to Service translation server (LoST-server).
The standardization for NG911/NG112 requires the calling device, also called endpoint, to convey the actual physical location during an emergency call. The calling device is further required to contact a mapping service based on the latest location information in order to obtain routing information during start-up and immediately before the emergency call set-up, and to validate the latest location information to ensure that the provided physical location is a valid and existing civic address or map location during start-up and immediately before the emergency call set-up. While obtaining the routing information is done via the LoST-server, validation is done via a Location Validation Function server (LVF-server) wherein the obtaining of the routing information and the validating of the latest location information may be done by the mapping service comprising the LoST-server and the LVF-server. If the endpoint fails to contact the mapping service in time before an emergency call, the endpoint must use cached data.
In case of network environments, where the endpoint, which may be in the form of a SIP endpoint contacts the mapping service via a server, which may be in a form of a SIP-server, the server contacts the mapping service on behalf of the registered endpoint. Updating the location information cached by the server and/or by the endpoint may be achieved by conveying the physical location of the endpoint to the server periodically to keep the server updated before an emergency call is set up. For periodically updating the location information cached by the server and/or by the device, a viable location source is required. Occasionally, the location source may be considered not to be viable. For example:                the location source does not respond to enquiries of the server and/or of the device,        the location source does not send information in a timely manner, for example within a periodic time interval,        the location source declares itself to not be viable,        the location source provides a null location which is not a valid location information,        the location source ceases to provide location information, and        the location source provides an unrealistic location.        
In the case of a not viable location source delivering not valid location information, one way of improving the accuracy of the location information is to attach an expiration date to the conveyed location information. The expiration time may be computed and associated with a location report received from a tracked entity as disclosed in US 2003/0135486 A1. An analysis of a history of previous location reports, here, is utilized to estimate the relevance of future location reports over time. By using the computed expiration time, an expiration time value acts as a threshold that controls the shape of a relevance degradation curve of a location report. In KR 20040092579, a method for correcting a location estimation error of a user equipment in a CDMA (Code Division Multiple Access) system is described, wherein an accurate location of a user terminal is estimated by correcting a location estimation error generated by a repeater. If a Base Transceiver Station (BTS) receives a message of an access channel for location registration of a user equipment from a core network, the BTS detects timing when the message of the random access channel is received, adds repeater pass path information to the message of the random access channel, and transmits the message to a Base Station Controller (BSC). The BTS searches for a repeater pass path of a signal received from the user equipment by using a stored message. The BSC estimates the location of the user equipment by using the retrieved repeater pass path information and error information of the repeater.
While this prior art addresses the accuracy of future location information based on stored location information presumed to be viable, these location estimate methods fail if the cached location information, on which the estimated location is based, is itself not viable or not valid.